Radial compressors convert mechanical energy into pressure energy by utilizing the centrifugal acceleration. Radial compressors essentially comprise a rotor, which is fastened to a driving shaft, a diffuser and a casing. The rotor has a plurality of curved blades. Depending on the intended use, the mechanical design of the rotor is effected like a closed or half-open rotor. In closed rotors, the blades are provided with a cover disk; in half-open rotors, the blades have a free outer edge.
The delivery gas is drawn in approximately in the center of the compressor and is compressed by the centrifugal force, also assisted by the curved shape of the blades, and accelerated outward. In the circumferentially arranged diffuser, the kinetic energy is mostly converted into additional pressure and the deliver gas is further compressed.
The energy conversion in radial compressors is associated with corresponding flow, friction and gap losses, for which reason radial compressors have a curved characteristic. In addition to a high efficiency, a stable characteristic is therefore aimed at, said characteristic being distinguished by an increasing delivery pressure at a decreasing delivery flow. However, the operating range of a radial compressor is restricted by the “surge limit”. This is generally the point of the characteristic having the smallest delivery quantity. The radial compressor can no longer be used on the other side of the surge limit, for the flow separates from the blades and stable operation can no longer be ensured.
The problem of stabilizing the characteristic of a radial compressor is treated, for example, in DE 42 14 753 A1. This document discloses a radial compressor rotor according to the preamble. The blades of this rotor are provided with through-holes, through which the delivery gas is fed from a convex blade pressure side to a concave blade suction side, such that the vortices which are formed on the blade suction side at small volumetric flows and high pressure ratios are removed.
Documents WO 2005/090794 A and U.S. Pat. No. 6,588,485 B1 have already disclosed radial compressor rotors having double-curved sections of the surface. In these embodiments, the entire surface is designed as a sculptured surface, a factor which firstly is complicated with regard to the description of the geometry and secondly involves a high production cost. DE 897 470 C has already disclosed a double-curved surface of a compressor blade mentioned at the beginning, produced by means of a crowned surface of a milling cutter. A blade produced in such a way cannot take into account the complexity of a three-dimensional flow.